1. Field of the Invention
This invention relates to a method and apparatus for image processing, and more particularly to a method and apparatus for image processing that distinguishes between alphanumeric symbols on a white background and those on a mesh pattern and performs individual image data processing.
2. Discussion of the Background
A recent trend in image processing is to have high performance capabilities and increased functional capabilities. Accordingly, many image processing apparatuses are now capable of performing high-definition image processing of input image data. To achieve a high-definition image processing performance, techniques for distinguishing between data of alphanumeric symbols and of a photograph are provided in the image processing apparatuses.
For example, an image reading apparatus disclosed in Japanese Laid Open Patent Application No. 03-63887 (1991) is capable of a high-definition image reproduction processing that distinguishes between alphanumeric symbols and photographs by judging differences in colors.
As another example, an image processing method disclosed in Japanese Laid Open Patent Application No. 01-137378 (1989) is capable of clearly reproducing a line image of an alphanumeric symbol with a clear edge in a binary form, and a halftone image such as a photograph using an artificial halftone in a binary form with a noise-reduced shape. This technique uses extracted density variations and selects different thresholds in accordance with the extracted density variations.
These conventional techniques improve image quality in reproduced images. However, these techniques are not capable of distinguishing between alphanumeric symbols on a white background, those on a mesh pattern, and design patterns. This is because the technique described in 03-63887 (1991) simply changes a threshold value of a Laplacian data unit, and the technique described in 01-137378 (1989) simply changes processing in accordance with color levels. Accordingly, these techniques are not capable of appropriately performing individual processing of alphanumeric symbols on a white background, those on a mesh pattern, and design patterns.
There is presently no image processing apparatus that is capable of distinguishing between alphanumeric symbols on a white background, those on a mesh pattern, and design patterns, and that appropriately performs individual processing of these different types of image data.